This invention relates generally to computed tomography (CT) imaging and more particularly, to verification of cable interconnection in a CT imaging system.
In at least one known CT system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the "imaging plane". The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a "view". A "scan" of the object comprises a set of views made at different gantry angles during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object.
One method for reconstructing an image from a set of projection data is referred to in the art as the filtered backprojection technique. This process converts the attenuation measurements from a scan into integers called "CT numbers" or "Hounsfield units", which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
To reduce the total scan time required for multiple slices, a "helical" scan may be performed. To perform a "helical" scan, the patient is moved while the data for the prescribed number of slices is acquired. Such a system generates a single helix from a one fan beam helical scan. The helix mapped out by the fan beam yields projection data from which images in each prescribed slice may be reconstructed. In addition to reduced scanning time, helical scanning provides other advantages such as improved image quality and better control of contrast.
In helical scanning, and as explained above, only one view of data is collected at each slice location. To reconstruct an image of a slice, the other view data for the slice is generated based on the data collected for other views. Helical reconstruction algorithms are known, and described, for example, in C. Crawford and K. King, "Computed Tomography Scanning with Simultaneous Patient Translation," Med. Phys. 17(6), November/December 1990.
At least one known imaging system is used to generate images of a heart of a patient to detect coronary artery calcification (CAC). The CAC is used to identify evidence of coronary atherosclerosis in the heart. In order to identify CAC in the image data, data is collected at specific times during a cycle of the heart. One known imaging system utilizes an EKG signal from the patient to time the collection of the data. As a result, images may be generated for specific times, for example during a systolic condition, so that heart motion is minimized. To date, the EKG signal is generated using EKG electrodes which are applied to the patient and connected to the imaging system after the patient was placed on a table of the imaging system. As a result, the setup time is increased and throughput of the imaging system is negatively impacted. In addition, if the EKG signal cable is improperly connected or fails, the imaging system will be unable to generate the properly timed images. Consequently, the scan will be forced to be repeated increasing x-ray dosage to the patient.
It would be desirable to provide a system which verifies proper connection of the EKG signal before scanning of the patient. It also would be desirable that such a system detect failures of an EKG signal cable during and after scanning of the patient without significantly increasing the cost of the imaging system.